Hypokinetic dysarthria means “lack of movement articulation disorder.” About 98% of cases are associated with Parkinson's disease. It can also be caused by anti-psychotic medications or head injuries. Not all Parkinson's patients experience speech impairment; of Parkinson's patients with speech impairment, not all have hypokinetic dysarthria, e.g., some experience language or cognitive dysfunction (dementia) affecting their speech.
Parkinson's disease is a degenerative disorder of the central nervous system, resulting from decreased stimulation of the motor cortex by the basal ganglia, normally caused by the insufficient formation and action of the neurotransmitter dopamine. Examples of the resulting lack of motor (muscle) movement include a Parkinson's patient thinking that he is moving his legs three feet, but his legs only move three inches. Walking becomes a shuffling gait with short steps and feet barely leaving the ground. Another Parkinson's patient may think she is smiling, but her face is actually an expressionless mask.
Diminished speech motor activity in hypokinetic dysarthria results in decreased vocal volume and in decreased articulation. Speech becomes unintelligible mumbling. Other symptoms of hypokinetic dysarthria include monopitch and monoloudness; pallilalia, or the compulsive repetition of syllables; and “articulatory undershoot” or lack of articulation.
The speaking rate of persons with hypokinetic dysarthria is complex:                “Bradykinesia (reduced speed of muscles) associated with Parkinson's disease causes difficulty in the initiation of voluntary speech. This can result in delay in starting to talk as well as very slow speech . . . there may be freezing of movement during speech. Rigidity can also occur. Additionally, Parkinson's patients have reduced loudness, imprecise consonant production, reduced pitch variability and festinating speech. The latter can result in extremely fast speech together with short rushes of speech.” (Patrick McCaffrey, Ph.D, “Dysarthria: Characteristics, Prognosis, Remediation”; http://www.csuchico.edu/˜pmccaffrey//syllabi/SPPA342/342unit14.html).        
In other words, hypokinetic dysarthria speech can be both abnormally slow and fast. The patient may start speaking slowly or with difficulty, but then speaking rate accelerates (“festinates”) until it is unintelligible.
Parkinson's is typically treated with medications and/or surgery (deep brain stimulation). Medications become less effective as the disease progresses, including less effect on speech. Surgery can improve some symptoms of Parkinson's while making speech worse.
For an overview of treatments for hypokinetic dysarthria, see A M Johnson, PhD, S G Adams, PhD; “Nonpharmacological Management of Hypokinetic Dysarthria in Parkinson's Disease”; Geriatrics & Aging, 2006 Feb. 14, http://www.medscape.com/viewarticle/521623).
A variety of voice amplifiers are available, such as the widely used ChatterVox. But these increase vocal volume without increasing clarity, so the result too often is just a louder mumble.
The most widely practiced treatment for speech disorders associated with Parkinson's is Lee Silverman Voice Therapy (LSVT). This speech therapy trains Parkinson's patients to increase vocal volume by increasing respiration activity and vocal fold activity. The result is improved volume and, as a side effect, improved articulation. In general, LSVT is more successful with mild to moderate Parkinson's patients and ineffective with severe patients. LSVT has several limitations. It requires speech motor awareness and control, problems for persons who are losing motor awareness and control. It is also limited by dual-tasking or the problem of thinking about how you're talking at the same time that you're thinking about what you're saying. Dual-tasking is difficult for healthy persons, but the cognitive impairments associated with Parkinson's make LSVT difficult for many Parkinson's patients, and impossible for severe patients.
Pacing boards, with which a user taps a series of squares as she produces each syllable, are sometimes used to help patients speak at a steady speaking rate, but also suffer from the dual-tasking problem. Speech with a pacing board also sounds abnormal.
Delayed auditory feedback (DAF), an electronic device in which the user hears his voice in headphones delayed a fraction of a second, for the purpose of slowing speaking rate, has been tried with Parkinson's patients. A summary of this research concluded that, “results were generally mixed” (Blanchet, Paul; “Treating Fluency and Speech Rate Disorders in Individuals with Parkinson's Disease: The Use of Delayed Auditory Feedback (DAF),” Journal of Stuttering, Advocacy & Research, 1 (2006), page 83).
Frequency-altered auditory feedback (FAF), an electronic device in which the user hears her voice in headphones altered in pitch or frequency (i.e., there are two types of FAF), has also been tried with Parkinson's patients. Anja Lowit and Bettina Brendel of Scotland's Strathclyde University found no significant results for +0.5 octave pitch-shifting FAF (shifting the pitch of the users' voices up a half octave) with Parkinson's patients. Six subjects had normal speech intelligibility, and ten subjects had speech scores below the normal range (“low intelligibility group”), but weren't severely impaired (they just were out of the normal range). (“The response of patients with Parkinson's Disease to DAF and FSF,” Stammering Research, Vol. 1., No. 1, April 2004.)
Another study used changing pitch-shifting FAF with Parkinson's patients to test their ability to alter their vocal pitch when making an “ah” sound. It found Parkinson's patients to be slower than controls when the FAF changed most rapidly. This study didn't investigate whether FAF improved users' speech. (Swathi Kiran and Charles R. Larson, “Effect of Duration of Pitch-Shifted Feedback on Vocal Responses in Patients With Parkinson's Disease,” Journal of Speech, Language, and Hearing Research, Vol. 44, 975-987, October 2001.)
A study at Rush University Medical Center, initiated Jun. 18, 2007, is testing a device with DAF and FAF with Parkinson's patients (Emily Wang and Leo Verhagen, “Improve Speech Using an in-the-Ear Device in Parkinson's Disease (MJFFSpeech),” http://clinicaltrials.gov/ct/show/NCT00488657?order=1). The device, called SpeechEasy, provides DAF and frequency-shifting FAF. A pilot study found that “Seven of the eight PD patients made significant improvement in their speech, and they were much easier to understand when they used the device.” The next phase of the study will test the device with 120 patients.
Jessica Huber, a speech-language pathologist at Purdue University, found that “multitalker babble noise” (similar to twenty unintelligible conversations in a room) increased Parkinson's patients' vocal volume 10 dB. She plans to develop a wearable electronic device that switches on this noise when the user talks. (“New technology helps Parkinson's patients speak louder,” http://www.purdue.edu/uns/x/2009b/090825HuberParkinsons.html, Aug. 25, 2009).
There is a need for an invention to induce persons with hypokinetic dysarthria to speak with increased speech motor activity, with the result that their speech is more intelligible, without devoting mental effort to speech motor activities that are normally automatic and unconscious.